Read John Krasinski's lips: He's in it to win it.
Fallon kicked it off with a heartfelt rendition of Melissa Manchester's "Don't Cry Out Loud. "That was really beautiful," Krasinski said, pretending to be choked up. Then he threw down the gauntlet with Katy Perry's "Teenage Dream," shimmying and unbuttoning his jacket.
"Fake breathing at the end and everything," a respectful Fallon noted.
They continued to duel, with Fallon lip-syncing Das EFX's "They Want EFX" and "Somewhere Over the Rainbow," and Krasinski doing Run DMC's "Peter Piper." But he really brought the house down with a throbbing version of Boyz II Men's "I'll Make Love to You."To the Roots's and audience's delight, Krasinski went there -- grabbing his fake earpiece, tearing off his jacket, loosening his tie. And at the end, he beckoned Fallon over to fake-sing together: "I'll make love to you, like you want me to!"
Watch out Justin Timberlake… you might need a new BFF.